Organic acids are widely used in industrial fields. For example, lactate is an organic acid that is broadly used in various industrial fields such as food, pharmaceutics, chemicals, and electronics. Lactate is a low-volatile material that is colorless, odorless, and water-soluble. Lactate is non-toxic to the human body and thus may be used as a flavoring agent, a taste agent, or a preserving agent. Additionally, lactate is an environment-friendly alternative polymer material and a raw material of a polylactic acid (PLA), which is a biodegradable plastic.
Organic acids may be dissociated into hydronium ions and their own anions at a higher pH than their own dissociation constant (pKa), for example, under a neutral condition (e.g., a pH of about 7). Organic acids (e.g., lactic acid) may be present in the form of a free acid without an electromagnetic force at a pH lower than its own pKa value. The anion of an organic acid may not be permeable with respect to a cell membrane; however, the organic acid may be permeable with respect to the cell membrane when the organic acid is present in the form of a free acid. Thus, an organic acid in a free acid form may flow into the cells from extracellular environments where the concentration of the organic acid is high, thus lowering intercellular pH level.
Therefore, to produce an organic acid present as negative ions requires an additional isolation process involving the addition of a salt. Furthermore, cells lacking acid resistance may become inactive and nonviable under acidic conditions, such as in the case of lactic acid buildup within a cell. Thus, there is a need for microorganisms that are acid tolerant. This invention provides such microorganisms.